This section provides background information related to the present disclosure which is not necessarily prior art. This section also provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
As a result of environmental and other concerns, plastic containers, more specifically polyester and even more specifically polyethylene terephthalate (PET) containers are now being used more than ever to package numerous commodities previously supplied in glass containers. Manufacturers and fillers, as well as consumers, have recognized that PET containers are lightweight, inexpensive, recyclable and manufacturable in large quantities.
Blow-molded plastic containers have become commonplace in packaging numerous commodities. PET is a crystallizable polymer, meaning that it is available in an amorphous form or a semi-crystalline form. The ability of a PET container to maintain its material integrity relates to the percentage of the PET container in crystalline form, also known as the “crystallinity” of the PET container. The following equation defines the percentage of crystallinity as a volume fraction:
      %    ⁢                  ⁢    Crystallinity    =            (                        ρ          -                      ρ            a                                                ρ            c                    -                      ρ            a                              )        ×    100  where ρ is the density of the PET material; ρa is the density of pure amorphous PET material (1.333 g/cc); and ρc is the density of pure crystalline material (1.455 g/cc).
Container manufacturers use mechanical processing and thermal processing to increase the PET polymer crystallinity of a container. Mechanical processing involves orienting the amorphous material to achieve strain hardening. This processing commonly involves stretching an injection molded PET preform along a longitudinal axis and expanding the PET preform along a transverse or radial axis to form a PET container. The combination promotes what manufacturers define as biaxial orientation of the molecular structure in the container. Manufacturers of PET containers currently use mechanical processing to produce PET containers having approximately 20% crystallinity in the container's sidewall.
Thermal processing involves heating the material (either amorphous or semi-crystalline) to promote crystal growth. On amorphous material, thermal processing of PET material results in a spherulitic morphology that interferes with the transmission of light. In other words, the resulting crystalline material is opaque, and thus, generally undesirable. Used after mechanical processing, however, thermal processing results in higher crystallinity and excellent clarity for those portions of the container having biaxial molecular orientation. The thermal processing of an oriented PET container, which is known as heat setting, typically includes blow molding a PET preform against a mold heated to a temperature of approximately 250° F.-350° F. (approximately 121° C.-177° C.), and holding the blown container against the heated mold for approximately two (2) to five (5) seconds. Manufacturers of PET juice bottles, which must be hot-filled at approximately 185° F. (85° C.), currently use heat setting to produce PET bottles having an overall crystallinity in the range of approximately 25%-35%.
Unfortunately, with some applications particularly those relating to high temperature food products (i.e. applesauce, pasta sauces, salsa, etc.) where the product is packaged and/or dispensed at high temperatures, it is often desirable to package these products in containers having wide mouth finish openings to permit convenient access to the product using a spoon or other cooking implement. These wide mouth finish openings, typically regarded as those greater than about 63 mm in diameter, must withstand contact with product temperatures up to about 205 deg F. and maintain functional performance such as seal integrity and recommended closure removal torque between the neck finish and closure cap.
In conventional applications, neck finishes were injected and crystallized to meet the required finish integrity and crystallinity at elevated temperatures. This approach was less economical due to low injection cavitation and the need for secondary processing to crystallize the neck finish after the preform part was produced.
However, today, technology has advanced that allows the neck finish to be blow molded, if sufficient structural integrity can be achieved in these wide mouth applications. That is, the goal would be to blow mold a container having a neck finish that achieves a crystallinity level greater than about 25%.
Conventionally, use of a closure cap on the neck finish, in high temperature food product applications with crystallinity levels greater than about 25%, causes inwardly-directed forces to the finish. When the neck finish comes in contact with the hot filled product thereafter, the neck finish becomes less rigid. Additionally, post pasteurization (where hot water spray, usually at or slightly above the product fill temperature, is applied on the container over a specified time (depending on customer requirement)) is requiring the neck finish to hold it shaped over a long period prior to post cooling. The combination of reduced rigidity, heat time duration, and the inward force from the closure, results in finish movement which then reduces the closure removal torque and possibly the seal integrity.
Therefore, although to date, preform design, mold temperature, and processing have produced blown neck finishes with an average crystallinity above 25%, it appears that the neck finish continues to experience disadvantageous movement resulting in low removal torque.
For at least this reason, the principles of the present teachings provide an improved neck finish for use in a container that provides improved structural integrity, especially in application of wide mouth container openings having average crystallinity above 25% and high temperature exposure. It should be appreciated that the principles of the present teachings have utility in a wide range of applications and uses, and thus the present disclosure should not be regarded as limited to only wide mouth opening containers, containers having an average crystallinity above 25%, or containers having high temperature exposure.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.